A Comparison of Retrieved Mass-Diameter Relationships in Snowfall from Radar and Ice Water Content Measurements

Mass to diameter (m-D) relationships for ice particles in the form aD^b are used to compute bulk microphysical properties, such as radar reflectivity (Z) and Ice Water Content (IWC) from particle size distributions (PSDs). The a and b values required to compute Z and IWC should be common properties of the PSD, but parameters retrieved from Z and IWC measurements tend to produce inconsistent results, and the parameters retrieved from one bulk property can not adequately recreate the measurement of another. In this study, we compare a and b mass parameters retrieved from collocated PSD, Z, and IWC measurements of synoptic snowstorms during three days of the Global Precipitation Measurement (GPM) Cold Season Experiment (GCPEx). Five-second PSD averages are collected by a Cloud Imaging Probe and a High Volume Precipitation Spectrometer aboard the University of North Dakota UND Citation. IWC is inferred from a Nevzorov Total Water Content probe in regions with minimal liquid water, as detected by a King Liquid Water Content probe. Reflectivity measurements come from a ground based WKR C-Band radar and are matched to Citation measured PSDs within a ±three minute window and a <500 meter radius of influence. Parameter a tends to decrease with the bth moment of the PSD, and this relationship gets steeper with increasing values of b. The difference between mass parameter a retrieved from Z and IWC methods varies with b and is minimized around b=2.3. Implications for improved remote sensing retrievals of IWC will be discussed.